U.S. patent application number 12/909084 was filed with the patent office on 2011-02-10 for pet polymer with improved properties.
This patent application is currently assigned to EASTMAN CHEMICAL COMPANY. Invention is credited to Frederick Leslie Colhoun, Perry Michael Murdaugh, SR..
Application Number | 20110031210 12/909084 |
Document ID | / |
Family ID | 37786917 |
Filed Date | 2011-02-10 |
United States Patent
Application |
20110031210 |
Kind Code |
A1 |
Colhoun; Frederick Leslie ;
et al. |
February 10, 2011 |
PET Polymer with Improved Properties
Abstract
Polyester compositions having desirable injection molding
properties and that retain good crystallization rates and natural
stretch ratio characteristics are described. These polyesters are
suitable for the manufacture of beverage containers, bulk
continuous filaments, and other articles that can benefit from such
improved properties.
Inventors: |
Colhoun; Frederick Leslie;
(Kingsport, TN) ; Murdaugh, SR.; Perry Michael;
(Lexington, SC) |
Correspondence
Address: |
BETTY JOY BOSHEARS;EASTMAN CHEMICAL COMPANY
P.O. BOX 511
KINGSPORT
TN
37662
US
|
Assignee: |
EASTMAN CHEMICAL COMPANY
Kingsport
TN
|
Family ID: |
37786917 |
Appl. No.: |
12/909084 |
Filed: |
October 21, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11254407 |
Oct 20, 2005 |
|
|
|
12909084 |
|
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|
|
Current U.S.
Class: |
215/373 ;
264/540; 428/35.7; 524/605; 525/437; 528/308.1 |
Current CPC
Class: |
Y10T 428/1352 20150115;
C08G 63/183 20130101; C08L 67/02 20130101; C08L 2666/02 20130101;
C08L 67/02 20130101; C08L 2666/02 20130101; C08L 67/025 20130101;
C08L 67/025 20130101 |
Class at
Publication: |
215/373 ;
528/308.1; 525/437; 524/605; 428/35.7; 264/540 |
International
Class: |
B65D 1/02 20060101
B65D001/02; C08G 63/183 20060101 C08G063/183; C08L 67/02 20060101
C08L067/02; B32B 1/02 20060101 B32B001/02; B29C 49/08 20060101
B29C049/08 |
Claims
1. A polyester comprising: i) a carboxylic acid component
comprising at least 90 mol % terephthalic acid residues and from 0
to 10 mol % of carboxylic acid comonomer residues; ii) a hydroxyl
component comprising from 90 to 95 mol % ethylene glycol residues
and additional hydroxyl residues in an amount from 5 to 10 mol %;
wherein the additional hydroxyl residues are chosen from a)
diethylene glycol residues and b) mixtures of diethylene glycol
residues and hydroxyl comonomer residues; based on 100 mol % of
carboxylic acid component residues and 100 mol % of hydroxyl
component residues in the polyester; wherein at least one of the
carboxylic acid and hydroxyl components comprises comonomer
residues, the molar ratio of the total comonomer residues to
diethylene glycol residues being 1.3:1.0 or greater; and wherein
the polyester comprises less than 2.3 mol % of diethylene glycol
and has an intrinsic viscosity greater than 0.40 dL/g and less than
0.80 dL/g
2. A polyester according to claim 1, wherein the carboxylic acid
comonomer is chosen from phthalic acid, isophthalic acid,
(C.sub.1-C.sub.4) dialkyl esters of isophthalic acid,
naphthalene-2,6-dicarboxylic acid, (C.sub.1-C.sub.4) dialkyl esters
of naphthalene 2-6-dicarboxylic acid, cyclohexanedicarboxylic acid,
cyclohexanediacetic acid, diphenyl-4,4'-dicarboxylic acid, succinic
acid, glutaric acid, adipic acid, azelaic acid, and sebacic acid;
or wherein the hydroxyl comonomer is chosen from triethylene
glycol, 1,4-cyclohexanedimethanol, propane-1,3-diol,
butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol,
3-methylpentanediol-(2,4), 2-methylpentanediol-(1,4),
2,2,4-trimethylpentane-diol-(1,3), 2,5-ethylhexanediol-(1,3),
2,2-diethyl propane-diol-(1,3), hexanediol-(1,3),
1,4-di-(hydroxyethoxy)-benzene,
2,2-bis-(4-hydroxycyclohexyl)-propane,
2,4-dihydroxy-1,1,3,3-tetramethyl-cyclobutane,
2,2-bis-(3-hydroxyethoxyphenyl)-propane, and
2,2-bis-(4-hydroxypropoxyphenyl)-propane.
3. A polyester according to claim 2, wherein the carboxylic acid
comonomer is chosen from isophthalic acid and naphthalene
2-6-dicarboxylic acid; or wherein the hydroxyl comonomer is
cyclohexane dimethanol.
4. A polyester according to claim 1, wherein the polyester
comprises less than 2.0 mol % of diethylene glycol.
5. A polyester according to claim 1, wherein the polyester has an
intrinsic viscosity greater than 0.65 dL/g and less than 0.77
dL/g.
6. A polyester according to claim 1, wherein the polyester has an
intrinsic viscosity greater than 0.65 dL/g and less than 0.76
dL/g.
7. A polyester according to claim 1, comprising: i) a carboxylic
acid component comprising at least 90 mol % terephthalic acid
residues and up to 10 mol % of carboxylic acid comonomer residues;
ii) a hydroxyl component comprising from 90 to 95 mol % ethylene
glycol residues and additional hydroxyl residues in an amount from
5 to 10 mol %%; wherein the additional hydroxyl residues are chosen
from a) diethylene glycol residues and b) mixtures of diethylene
glycol residues and hydroxyl comonomer residues; based on 100 mol %
of carboxylic acid component residues and 100 mol % of hydroxyl
component residues in the polyester; wherein at least one of the
carboxylic acid and hydroxyl components comprises comonomer
residues, the molar ratio of the total comonomer residues to
diethylene glycol residues being 1.5:1.0 or greater; and wherein
the polyester comprises less than 1.6 mol % of diethylene glycol
and has an intrinsic viscosity of less than 0.76 dL/g.
8. A polymer blend comprising a polyester as claimed in claim 1 and
one or more additional polymers.
9. A composition comprising a polyester as claimed in claim 1 and
one or more additives.
10. A composition according to claim 9, wherein the one or more
additives are chosen from colorants, pigments, glass fibers, impact
modifiers, antioxidants, surface lubricants, denesting agents, UV
light absorbing agents, metal deactivators, fillers, nucleating
agents, stabilizers, flame retardants, reheat aids, crystallization
aids, acetaldehyde reducing compounds, recycling release aids,
oxygen scavenging materials, platelet particles, and mixtures
thereof.
11. An article comprising a polyester as claimed in claim 1.
12. An article according to claim 11, wherein the article is a
molded, extruded, or a thermoformed article.
13. An article according to claim 11, wherein the article is a
beverage container or a beverage container preform.
14. An article according to claim 12, wherein the article is a
bottle.
15. A process for producing an container comprising: feeding
crystallized particles comprising a polyester as claimed in claim 1
to an extrusion zone; melting the particles; forming a sheet or
molded part from the molten extruded polyester; and processing the
sheet or molded part to make a container.
16. A polyester according to claim 1, comprising: i) a carboxylic
acid component comprising 100 mol % terephthalic acid residues; ii)
a hydroxyl component comprising from 90 to 95 mol % ethylene glycol
residues and additional hydroxyl residues in an amount from 5 to 10
mol %; wherein the additional hydroxyl residues are diethylene
glycol residues and hydroxyl comonomer residues; based on 100 mol %
of carboxylic acid component residues and 100 mol % of hydroxyl
component residues in the polyester; wherein the molar ratio of the
hydroxyl comonomer residues to diethylene glycol residues being
1.5:1.0 or greater; and wherein the polyester comprises less than
1.6 mol % of diethylene glycol and has an intrinsic viscosity of
less than 0.76 dL/g.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of application Ser. No.
11/254,407, entitled "PET Polymers With Improved Properties" which
was filed on Oct. 20, 2005, all of which is hereby incorporated by
this reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention is directed to certain polyesters
having desirable injection molding properties while retaining good
crystallization rates and natural stretch ratio characteristics.
These polyesters may be advantageously used, for example, in water
applications, for instance, for the manufacture of beverage
containers. These polyesters can also be used in the manufacture of
bulk continuous filaments, and other articles that can benefit from
such properties.
BACKGROUND
[0003] Poly(ethylene terephthalate) copolymers, commonly referred
to as PET polymers, are widely used in the manufacture of light
weight containers for carbonated and non-carbonated drinks, juice,
water, jellies, marmalades, and other similar foodstuffs. Packages
made by stretch blow molding of PET polymers possess excellent
mechanical properties, such as high strength and shatter
resistance, as well as good gas barrier properties.
[0004] Typically, to form plastic containers, the PET polymer is
extruded and formed into chips or pellets. The pellets are then
melted and used to make a container preform by injection molding.
The preform is subsequently reheated and stretched-blown into a
mold, which provides the final shape of the container. The stretch
blow molding step causes biaxial orientation of the polyester to
occur at least in some parts of the container and provides strength
to the container so that it can resist deformation from internal
pressure during use and can adequately contain the fluid.
[0005] There are three key characteristics of PET polymers that are
relevant to making containers by stretch blow molding, namely,
their natural stretch ratio, their crystallization rate, and the
rate at which they fill injection molds.
[0006] The natural stretch ratio is an inherent property of a
polymer and is a measure of how much the preform can stretch to
take the shape of the final article. In the present Examples, the
free blow volume of a given polymer is used as a measure of the
natural stretch ratio of that polymer. The natural stretch ratio of
a polymer influences the design of the preform by determining its
stretch ratio limitations. Due to the high cost of injection mold
tooling, new PET resins that perform well with existing preform
designs can be used. Resins with very low natural stretch ratios
generally create processing problems during stretch blow molding,
while resins with very high natural stretch ratios generally yield
containers with poor physical properties if used in conjunction
with preform and bottle tooling.
[0007] The rate of crystallization of a PET polymer can influence
the clarity or transparency of the final article. Therefore,
controlling the rate of crystallization becomes relevant especially
when the application requires clear or transparent products.
Thermally induced crystallization tends to form large crystallites
in the polymer, resulting in haze. In order to minimize the
formation of crystallites and thus have clear preforms, the rate of
thermal crystallization needs to be slow enough so that preforms
with little or no crystallinity can be produced. However, if the
rate of thermal crystallization is too low, the production rates of
PET resin using solid state polymerization can be adversely
affected because PET needs to be crystallized prior to solid-state
polymerization.
[0008] The rate at which a polymer fills an injection mold is
directly related to its intrinsic viscosity. A lower viscosity
resin is generally desired because it will fill the injection mold
more easily, leading to a reduction in injection molding cycle time
and an increase in product output. Also, a lower viscosity resin
will reduce the injection pressure required to fill the mold in a
given time, reducing the wear and tear on the injection molding
machine. Therefore, manufacturing costs may be reduced for resins
with a lower intrinsic viscosity.
[0009] Unfortunately, improving one of these three
properties--natural stretch ratio, crystallization rate, or fill
injection rate--has normally resulted in detriment to one or both
of the remaining properties. For example, compositions with
suitably slow crystallization rates often require a higher
intrinsic viscosity to maintain an adequate natural stretch ratio,
which adversely impacts the fill time in injection molding.
BRIEF DESCRIPTION OF THE INVENTION
[0010] We have discovered a polyester composition having desirable
injection molding properties while retaining good crystallization
rates and natural stretch ratio characteristics.
[0011] In one embodiment, the present invention provides a
polyester comprising: [0012] i) a carboxylic acid component
comprising at least 90 mol % terephthalic acid residues and from 0
to 10 mol % of carboxylic acid comonomer residues; [0013] ii) a
hydroxyl component comprising at least 90 mol % ethylene glycol
residues and additional hydroxyl residues in an amount up to 10 mol
%; wherein the additional hydroxyl residues are chosen from [0014]
a) diethylene glycol residues and b) mixtures of diethylene glycol
residues and hydroxyl comonomer residues;
[0015] based on 100 mol % of carboxylic acid component residues and
100 mol % of hydroxyl component residues in the polyester; wherein
at least one of the carboxylic acid and hydroxyl components
comprises comonomer residues, the molar ratio of the total
comonomer residues to diethylene glycol residues being 1.3:1.0 or
greater; and wherein the polyester comprises less than 2.3 mol % of
diethylene glycol and has an intrinsic viscosity greater than 0.40
dL/g and less than 0.77 dL/g.
[0016] In another embodiment, the present invention provides a
polyester comprising: [0017] i) a carboxylic acid component
comprising 100 mol % terephthalic acid residues; [0018] ii) a
hydroxyl component comprising at least 90 mol % ethylene glycol
residues and additional hydroxyl residues in an amount up to 10 mol
%; wherein the additional hydroxyl residues are diethylene glycol
residues and hydroxyl comonomer residues;
[0019] based on 100 mol % of carboxylic acid component residues and
100 mol % of hydroxyl component residues in the polyester; wherein
the molar ratio of the hydroxyl comonomer residues to diethylene
glycol residues is 1.3:1.0 or greater; and wherein the polyester
comprises less than 2.3 mol % of diethylene glycol and has an
intrinsic viscosity greater than 0.40 dL/g and less than 0.80
dL/g.
[0020] In another embodiment, the present invention provides a
polyester comprising: [0021] i) a carboxylic acid component
comprising at least 90 mol % terephthalic acid residues and from 0
to 10 mol % of carboxylic acid comonomer residues; [0022] ii) a
hydroxyl component comprising at least 90 mol % ethylene glycol
residues and the remainder diethylene glycol residues;
[0023] based on 100 mol % of carboxylic acid component residues and
100 mol % of hydroxyl component residues in the polyester; wherein
the molar ratio of the carboxylic acid comonomer residues to
diethylene glycol residues is 1.3:1.0 or greater; and wherein the
polyester comprises less than 2.3 mol % of diethylene glycol and
has an intrinsic viscosity greater than 0.40 dL/g and less than
0.77 dL/g. In another embodiment, the hydroxyl component comprises
at least 98.4 mol % ethylene glycol residues and 1.6 mol % or less
of diethylene glycol residues. In other embodiments, the hydroxyl
component comprises from 0.5 to 2.3 mol % of diethylene glycol
residues, or from 0.5 to 1.6 mol % of diethylene glycol
residues.
[0024] In another embodiment, the present invention provides a
polyester wherein the carboxylic acid comonomer is chosen from
phthalic acid, isophthalic acid, (C.sub.1-C.sub.4) dialkyl esters
of isophthalic acid, naphthalene-2,6-dicarboxylic acid,
(C.sub.1-C.sub.4) dialkyl esters of naphthalene 2-6-dicarboxylic
acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid,
diphenyl-4,4'-dicarboxylic acid, succinic acid, glutaric acid,
adipic acid, azelaic acid, and sebacic acid; or wherein the
hydroxyl comonomer is chosen from triethylene glycol,
1,4-cyclohexanedimethanol, propane-1,3-diol, butane-1,4-diol,
pentane-1,5-diol, hexane-1,6-diol, 3-methylpentanediol-(2,4),
2-methylpentanediol-(1,4), 2,2,4-trimethylpentane-diol-(1,3),
2,5-ethylhexanediol-(1,3), 2,2-diethyl propane-diol-(1,3),
hexanediol-(1,3), 1,4-di-(hydroxyethoxy)-benzene,
2,2-bis-(4-hydroxycyclohexyl)-propane,
2,4-dihydroxy-1,1,3,3-tetramethyl-cyclobutane,
2,2-bis-(3-hydroxyethoxyphenyl)-propane, and
2,2-bis-(4-hydroxypropoxyphenyl)-propane.
[0025] In another embodiment, the carboxylic acid component of the
polyesters of the invention comprises from 1 to 10 mol % of
carboxylic acid comonomer. The polyesters can also comprise from 3
to 10 mol % of carboxylic acid comonomer or from 5 to 10 mol % of
carboxylic acid comonomer. In another embodiment, the hydroxyl
component of the polyesters of the invention comprises from 1 to 10
mol % of additional hydroxyl residues. The polyesters can also
comprise from 3 to 10 mol % of additional hydroxyl residues or from
5 to 10 mol % of additional hydroxyl residues.
[0026] In another embodiment, the polyesters of the invention
comprise less than 2.0 mol % of diethylene glycol. In yet another
embodiment, the polyesters of the invention comprise less than 1.6
mol % of diethylene glycol.
[0027] In another embodiment, the molar ratio of the total
comonomer residues to diethylene glycol residues in the polyesters
of the invention is 1.5:1.0 or greater.
[0028] In another embodiment, the intrinsic viscosity of the
polyesters of the invention is less than 0.79 dL/g. For example,
the intrinsic viscosity of the polyester particles can be less than
0.78 dL/g, or less than 0.77 dL/g, and even less than 0.76
dL/g.
[0029] Optionally, the polyesters of the invention contain less
than 2 ppm residual acetaldehyde (as measured by the French
National Standard Test). In another embodiment, the polyesters
contain less than 1 ppm residual acetaldehyde.
[0030] The polyesters of the invention can be made from virgin raw
materials or from recycled polyester polymers. In one embodiment of
the invention, the polyester is prepared from 75 wt % or greater
virgin raw materials.
[0031] The polyesters of the invention can be made by a number of
processes well known in the art. For example, the polyester polymer
can be produced by melt polymerization, optionally followed by
solid-state polymerization. Also, the polyester can either be
crystallized before or after the formation of pellets.
[0032] In one embodiment, the polyester polymer can be produced by
melt polymerization to a molecular weight suitable for container
applications, for example, with an intrinsic viscosity greater than
0.65 dL/g, then formed into particles, such as pellets, and
crystallized. If desired, the polyesters can also undergo the
removal of most of the residual acetaldehyde.
[0033] The polyesters of the invention can be used to manufacture
containers (e.g., bottles), sheets, films, trays, rods, tubes,
lids, filaments and fibers and other packaging items. In one
embodiment, the polyester polymers of the invention are used to
make uncarbonated water containers.
DEFINITIONS
[0034] Throughout the specification and claims, including the
detailed description below, the following definitions apply.
[0035] As used in the specification and the appended claims, the
singular forms "a", "an", and "the" include plural referents unless
the context clearly dictates otherwise. For example, reference to
processing or making a polymer, a preform, an article, a container,
or a bottle is intended to include the processing or making of
singular and a plurality of polymers, preforms, articles,
containers or bottles. References to a composition containing "an"
ingredient or "a" polymer is intended to include other ingredients
or other polymers, respectively, in addition to the one named. It
should also be noted that the term "or" is generally employed in
its sense including "and/or" unless the content clearly dictates
otherwise.
[0036] It is also to be understood that the mention of one or more
method steps does not preclude the presence of additional method
steps before or after the combined recited steps or intervening
method steps between those steps expressly identified. Moreover,
the lettering of process steps is a convenient means for
identifying discrete activities or steps, and unless otherwise
specified, recited process steps can be arranged in any
sequence.
[0037] The term residue as used herein, refers to the portion of a
compound that is incorporated into a polyester during
polycondensation.
[0038] The term carboxylic acid component as used herein, refers to
all carboxylic acid residues of a polyester.
[0039] The term hydroxyl component as used herein, refers to all
hydroxyl residues of a polyester.
[0040] The term carboxylic acid comonomer residue as used herein,
refers to any carboxylic acid residue, other than terephthalic acid
residues.
[0041] The term hydroxyl comonomer residue as used herein, refers
to any hydroxyl residue, other than ethylene glycol residues and
diethylene glycol residues.
[0042] The term total comonomer residues as used herein, refers to
the sum of carboxylic acid comonomer residues and hydroxyl
comonomer residues.
[0043] The intrinsic viscosity values described throughout this
application are set forth in dL/g units as calculated from the
inherent viscosity measured at 25.degree. C. in a 60/40 wt/wt
mixture of phenol/tetrachloroethane. The intrinsic viscosity of the
polyester is determined by the method described in U.S. Application
Publication No. 2005/0196566, which is hereby incorporated by
reference.
[0044] Other than in the operating examples, or where otherwise
indicated, all numbers expressing quantities used in the
specification and claims are to be understood as being modified in
all instances by the term "about." Accordingly, unless indicated to
the contrary, the numerical parameters set forth in the present
specification and attached claims are approximations that may vary
depending upon the desired properties sought to be obtained by the
present invention. It should be understood that the exact numerical
values disclosed also form embodiments of the invention. At the
very least, and not as an attempt to limit the application of the
doctrine of equivalents to the scope of the claims, each numerical
parameter should be construed in light of the number of reported
significant digits and by applying ordinary rounding
techniques.
[0045] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the invention are approximations,
the numerical values set forth in the specific examples are
reported as precisely as possible. Any numerical value, however,
inherently contain certain errors necessarily resulting from the
standard deviation found in their respective testing
measurements.
DETAILED DESCRIPTION OF THE INVENTION
[0046] The present invention is directed to certain polyesters
having desirable injection molding properties while retaining good
crystallization rates and natural stretch ratio
characteristics.
[0047] In one embodiment, the present invention provides a
polyester comprising: [0048] i) a carboxylic acid component
comprising at least 90 mol % terephthalic acid residues and from 0
to 10 mol % of carboxylic acid comonomer residues; [0049] ii) a
hydroxyl component comprising at least 90 mol % ethylene glycol
residues and additional hydroxyl residues in an amount up to 10 mol
%; wherein the additional hydroxyl residues are chosen from [0050]
a) diethylene glycol residues and b) mixtures of diethylene glycol
residues and hydroxyl comonomer residues;
[0051] based on 100 mol % of carboxylic acid component residues and
100 mol % of hydroxyl component residues in the polyester; wherein
at least one of the carboxylic acid and hydroxyl components
comprises comonomer residues, the molar ratio of the total
comonomer residues to diethylene glycol residues being 1.3:1.0 or
greater; and wherein the polyester comprises less than 2.3 mol % of
diethylene glycol and has an intrinsic viscosity greater than 0.40
dL/g and than less 0.77 dL/g.
[0052] In another embodiment, the present invention provides a
polyester comprising: [0053] i) a carboxylic acid component
comprising 100 mol % terephthalic acid residues; [0054] ii) a
hydroxyl component comprising at least 90 mol % ethylene glycol
residues and additional hydroxyl residues in an amount up to 10 mol
%; wherein the additional hydroxyl residues are diethylene glycol
residues and hydroxyl comonomer residues;
[0055] based on 100 mol % of carboxylic acid component residues and
100 mol % of hydroxyl component residues in the polyester; wherein
the molar ratio of the hydroxyl comonomer residues to diethylene
glycol residues is 1.3:1.0 or greater; and wherein the polyester
comprises less than 2.3 mol % of diethylene glycol and has an
intrinsic viscosity greater than 0.40 dL/g and less than 0.80
dL/g.
[0056] In another embodiment, the present invention provides a
polyester comprising: [0057] i) a carboxylic acid component
comprising at least 90 mol % terephthalic acid residues and from 0
to 10 mol % of carboxylic acid comonomer residues; [0058] ii) a
hydroxyl component comprising at least 90% ethylene glycol residues
and the remainder diethylene glycol residues;
[0059] based on 100 mol % of carboxylic acid component residues and
100 mol % of hydroxyl component residues in the polyester; wherein
the molar ratio of the carboxylic acid comonomer residues to
diethylene glycol residues is 1.3:1.0 or greater; and wherein the
polyester comprises less than 2.3 mol % of diethylene glycol and
has an intrinsic viscosity greater than 0.40 dL/g and less than
0.77 dL/g. In another embodiment, the hydroxyl component comprises
at least 98.0 mol % ethylene glycol residues and 2.0 mol % or less
of diethylene glycol residues. In another embodiment, the hydroxyl
component comprises at least 98.4 mol % ethylene glycol residues
and 1.6 mol % or less of diethylene glycol residues. In other
embodiments, the hydroxyl component comprises from 0.5 to 2.3 mol %
of diethylene glycol residues, or from 0.5 to 2.0 mol % of
diethylene glycol residues, or from 0.5 to 1.6 mol % of diethylene
glycol residues.
[0060] Typically, polyesters such as polyethylene terephthalate are
made by reacting a diol such as ethylene glycol with a dicarboxylic
acid as the free acid or its dimethyl ester to produce an ester
monomer or oligomers (esterification), which are then polycondensed
to produce the polyester. More than one type of dicarboxylic
residue can be used in the esterification reaction and the totality
of carboxylic acid residues forms the carboxylic acid component of
the polyester. Similarly, the totality of diol residues forms the
hydroxyl component of the polyester.
[0061] In the polyesters of the invention, the carboxylic acid
component comprises at least 90 mol % terephthalic acid residues,
which can be supplied by terephthalic acid or by other terephthalic
acid derivatives, such as, for example, (C.sub.1-C.sub.4) dialkyl
esters of terephthalic acid. The mole percent of all the compounds
containing at least one carboxylic acid group or derivatives
thereof that are in the product polyester add up to 100%. In the
polymers of the invention, the balance of carboxylic acid residues,
aside from terephthalic acid residues, are carboxylic acid
comonomer residues (from 0 to 10 mol %).
[0062] In the polyesters of the invention, the hydroxyl component
comprises at least 90 mol % ethylene glycol residues and additional
hydroxyl residues in an amount up to 10 mol %. The mole percent of
all the compounds containing hydroxyl group(s) or derivatives
thereof that become part of the product adds up to 100%. The mole
percent of the hydroxyl residues and carboxylic acid residues in a
product can be determined by proton NMR.
[0063] The reaction of the carboxylic acid component with the
hydroxyl component during the preparation of the polyester polymer
is not restricted to the stated stoichiometric mole percentages
since one may utilize a large excess of the hydroxyl component if
desired, e.g., on the order of up to 200 mole % relative to the 100
mole % of carboxylic acid component used. The polyester polymer
made by the reaction will, however, contain the stated amounts of
dicarboxylic acid residues and diol residues.
[0064] As mentioned previously, the carboxylic acid component of
the polyesters of the invention can also include one or more
additional carboxylic acid comonomers. Examples of compounds that
can provide carboxylic acid comonomer residues include
mono-carboxylic acid compounds, dicarboxylic acid compounds, and
compounds with a higher number of carboxylic acid groups. Examples
include aromatic dicarboxylic acids, for instance those having 8 to
14 carbon atoms; aliphatic dicarboxylic acids, for instance those
having 4 to 12 carbon atoms; or cycloaliphatic dicarboxylic acids,
for instance those having 8 to 12 carbon atoms. More specific
examples of modifier dicarboxylic acids include phthalic acid;
isophthalic acid; derivatives of isophthalic acid such as, for
example, (C.sub.1-C.sub.4) dialkyl esters of isophthalic acid;
naphthalene-2,6-dicarboxylic acid; derivatives of
naphthalene-2,6-dicarboxylic acid such as, for example,
(C.sub.1-C.sub.4) dialkyl esters of naphthalene 2-6-dicarboxylic
acid; cyclohexanedicarboxylic acid; cyclohexanediacetic acid;
diphenyl-4,4'-dicarboxylic acid; succinic acid; glutaric acid;
adipic acid; azelaic acid; and sebacic acid; and the like. In one
embodiment, isophthalic acid, naphthalene-2,6-dicarboxylic acid, or
cyclohexanedicarboxylic acid are used as carboxylic acid
comonomers. It should be understood that use of the corresponding
acid anhydrides, esters, and acid chlorides of these acids is
included in the term "carboxylic acid". It is also possible for
tricarboxyl compounds and compounds with a higher number of
carboxylic acid groups to modify the polyester. In one embodiment
of the invention, the carboxylic acid comonomers are chosen from
isophthalic acid and naphthalene-2,6-dicarboxylic acid.
[0065] In addition to ethylene glycol and diethylene glycol, the
hydroxyl component of the present polyester may include additional
mono-ols, diols, or residues with a higher number of hydroxyl
groups. Examples of compounds that can provide hydroxyl residues
include cycloaliphatic diols, for instance those having 6 to 20
carbon atoms or aliphatic diols, for instance those having 3 to 20
carbon atoms. More specific examples of such diols include
triethylene glycol; 1,4-cyclohexanedimethanol; propane-1,3-diol;
butane-1,4-diol; pentane-1,5-diol; hexane-1,6-diol;
3-methylpentanediol-(2,4); 2-methylpentanediol-(1,4);
2,2,4-trimethylpentane-diol-(1,3); 2,5-ethylhexanediol-(1,3);
2,2-diethyl propane-diol-(1,3); [0066] hexanediol-(1,3);
1,4-di-(hydroxyethoxy)-benzene;
2,2-bis-(4-hydroxycyclohexyl)-propane;
2,4-dihydroxy-1,1,3,3-tetramethyl-cyclobutane; [0067]
2,2-bis-(3-hydroxyethoxyphenyl)-propane; or
2,2-bis-(4-hydroxypropoxyphenyl)-propane. In one embodiment of the
invention, the hydroxyl comonomer is cyclohexanedimethanol.
[0068] In one embodiment, the carboxylic acid component of the
polyesters of the invention comprises from 0 to 10 mol % of
carboxylic acid comonomer, for example from 1 to 10 mol % of
carboxylic acid comonomer. The polyesters can also comprise from 3
to 10 mol % of carboxylic acid comonomer or from 5 to 10 mol % of
carboxylic acid comonomer. In another embodiment, the hydroxyl
component of the polyesters of the invention comprises from 1 to 10
mol % of additional hydroxyl residues. The polyesters can also
comprise from 3 to 10 mol % of additional hydroxyl residues or from
5 to 10 mol % of additional hydroxyl residues. In another
embodiment, if isophthalic acid residues are used as comonomer
residues, the hydroxyl component comprises a hydroxyl
comonomer.
[0069] The polyesters of the present invention typically contain a
lower mole percent of diethylene glycol (DEG) than many other
polyesters used in similar applications. Any method suitable for
reducing DEG content of polyester can be employed in the present
invention. Suitable methods include reducing the mole ratio of
diacid or diester relative to ethylene glycol in the esterification
or transesterification reaction; reducing the temperature of the
esterification or transesterification reaction, addition of
DEG-suppressing additives, including tetra-alkyl ammonium salts and
the like; and reduction of the DEG content of the ethylene glycol
that is recycled back to the esterification or transesterification
reaction.
[0070] In certain embodiments, the polyesters of the invention
comprise less than 2.0 mol % of diethylene glycol or less than 1.6
mol % of diethylene glycol. The minimization of the DEG content
allows for substitution with comonomers that could be more
effective in retarding the crystallization rate or provide other
beneficial characteristic to the polyester. In this manner, the
total amount of comonomer modification employed can be reduced.
[0071] We have found that an appropriate molar ratio of the total
comonomer residues to diethylene glycol residues in the polyesters
of the invention is 1.3:1.0 or greater. In another embodiment, the
molar ratio of the total comonomer residues to diethylene glycol
residues in the polyesters of the invention is 1.5:1.0 or greater,
for example, 1.9:1.0 or greater. In other embodiments, the mole
percent of the diethylene glycol residues plus the mole percent of
the total comonomer residues is greater than 4.0%; greater than
5.0%, or greater than 5.5%, or even greater than 6.0%.
[0072] We have found that minimizing the DEG content and
maintaining the molar ratios of comonomer to DEG mentioned above
allows a reduction in the pellet intrinsic viscosity while
maintaining desirable natural stretch ratio and container physical
properties. A reduction in the pellet inherent viscosity is
valuable in a number of ways. A lower viscosity resin will fill the
injection mold more easily, leading to a reduction in injection
molding cycle time and an increase in product output. Also, a lower
viscosity resin will reduce the injection pressure required to fill
the mold in a given time, reducing the wear and tear on the
injection molding machine. Therefore, manufacturing costs may be
reduced for resins with a lower intrinsic viscosity.
[0073] Accordingly, the intrinsic viscosity of the polyesters of
the invention can be less than 0.80 dL/g. For example, the
intrinsic viscosity of the polyester particles can be less than
0.79 dL/g, less than 0.78 dL/g, or less than 0.77 dL/g, and even
less than 0.76 dL/g. In another embodiment, the polyesters of the
invention have an intrinsic viscosity greater than or equal to 0.40
dL/g. However, polyesters with intrinsic viscosities lower than
0.65 dL/g may not be suitable for the preparation of some beverage
containers. The appropriate intrinsic viscosity can be chosen to
best fit the application for which the polyester is to be used.
Accordingly, in one embodiment, the polyesters of the invention
have an intrinsic viscosity greater than or equal to 0.65 dL/g. In
another embodiment of the invention, the polyesters have an
intrinsic viscosity greater than or equal to 0.69 dL/g. Suitable
intrinsic viscosities for the polyesters of the invention can be
achieved by appropriate manipulation of the molecular weight of the
polyester polymer chains.
[0074] Polyesters with intrinsic viscosities falling within a range
defined by any two intrinsic viscosity values recited in the
instant application are also within the scope of the present
invention. For example, a polyester can have an intrinsic viscosity
between 0.65 dL/g and 0.78 dL/g; or between 0.76 dL/g and 0.80
dL/g; or between 0.65 dL/g and 0.69 dL/g; etc.
[0075] During the molding or extrusion processes, acetaldehyde is
formed by thermal decomposition of the polyester. When the
polyester is formed into an article, the acetaldehyde in the
article walls could migrate into the contents of the article. Small
amounts of acetaldehyde adversely affect the flavor retaining
property of foods and beverages, and the fragrance retaining
property of foods, beverages, cosmetics, and other package
contents. For these reasons, it is desirable to minimize the
migration of acetaldehyde into package contents.
[0076] Therefore, in one embodiment, the polyesters of the
invention contain less than 5 ppm residual acetaldehyde (as
measured by the French National Standard Test). In another
embodiment, the polyesters contain less than 2 ppm residual
acetaldehyde or even less than 1 ppm residual acetaldehyde.
[0077] Acetaldehyde content can be successfully reduced in
crystalline PET compositions by solid state polymerization. Solid
state polymerization of PET polymers not only decreases its
acetaldehyde content but also decreases its tendency to form
acetaldehyde. Additionally, polyamides or other acetaldehyde
scavengers known in the art can be used to reduce the level of
acetaldehyde to an acceptable range.
[0078] The polyesters of the invention may be made by melting post
consumer recycled polyester polymer. However, the molecular weight
of bulk recycled polyester polymers can vary widely depending on
their source or their service requirement. Therefore, it is
desirable to use at least 75 wt % virgin polyester polymer when
recycled polyester polymers are employed. In general, a virgin
polyester polymer is made without post consumer recycled polymers,
but it may optionally contain scrap or regrind polymers.
[0079] The polyesters of the invention can be made by a number of
processes well known in the art. For example, the polyesters can be
produced by melt phase polymerization. If the polymers are to be
used to make plastic containers, polymerization is carried our to a
molecular weight suitable for said container applications, for
example by producing polymers having an intrinsic viscosity of at
least 0.65 dL/g. Melt phase polymerization can be followed by
process steps comprising, in no particular order, formation of
particles, such as pellets, crystallization, and optionally removal
of most of the residual acetaldehyde.
[0080] Various methods can be used for solidifying the polyester
polymer after melt phase polymerization. For example, molten
polyester polymer from the melt phase may be directed through a
die, or merely cut, or both directed through a die followed by
cutting the molten polymer. A gear pump may be used to drive the
molten polyester polymer through the die. However, instead of using
a gear pump, the molten polyester polymer may be fed into a single
or twin screw extruder and extruded through a die, optionally at a
temperature of 190.degree. C. or more at the extruder nozzle. Once
through the die, the polyester polymer can be drawn into strands,
contacted with a cool fluid, and cut into pellets, or the polymer
can be pelletized at the die head, optionally underwater. The
polyester polymer melt may be optionally filtered to remove
particulates over a designated size before being cut. Any
conventional hot pelletization or dicing method and apparatus can
be used, including but not limited to dicing, strand pelletizing
and strand (forced conveyance) pelletizing, pastillators, water
ring pelletizers, hot face pelletizers, underwater pelletizers and
centrifuged pelletizers.
[0081] The polyesters of the invention can also be made by using
solid state polymerization after melt polymerization. Crystalline
PET can be solid stated since crystalline PET has a well defined
melting point. In contrast, noncrystalline or amorphous
copolyesters cannot be solid stated since such copolyesters lack a
definite crystal structure and a well defined melting point and
thus melt during the solid stating process forming large
agglomerates. Therefore, if the length of the chain is going to be
increased by solid state polymerization in the polyesters of the
invention, the polyesters can be crystallized before hand.
[0082] Various methods and apparatuses can be used to crystallize
the polyesters of the invention. For example, the polyesters can be
thermally crystallized in a gas or a liquid. The crystallization
may occur in a mechanically agitated vessel, a fluidized bed, a bed
agitated by fluid movement, or in an unagitated vessel or pipe. The
polyesters can also be crystallized in a liquid medium above the
glass transition temperature of the polyester, typically between
140.degree. C. and 180.degree. C. The polyesters may also be strain
crystallized.
[0083] Typically, the polyester is crystallized to at least a 15%
degree of crystallization. Higher crystallization degrees can also
be used, for example at least 25%, or at least 30%, or at least
35%, or at least 40%. The polyesters of the invention can be
crystallized either before or after the formation of pellets.
[0084] Once crystallized pellets are obtained, they can be
transported to a machine for melt processing into the desired
shape, such as fibers, sheets for thermoforming into trays, or
preforms suitable for stretch blow molding into beverage or food
containers. Examples of beverage containers include containers such
as bottles having a volume of 3 liters or less, suitable for hot
fill, carbonated soft drinks, or water.
[0085] The present invention also provides a process for making a
polyester container, for example a preform or a beverage bottle,
comprising feeding crystallized polyester particles or pellets of
the invention to an extrusion zone, melting the particles in the
extrusion zone to form a molten polyester polymer composition, and
forming a sheet or a molded part from extruded molten polyester
polymer. The particles fed to the extrusion zone are normally dried
and typically have sufficient crystallinity to prevent them from
sticking to each other or to equipment during drying at a
temperature ranging from 140.degree. C. to 180.degree. C. Moreover,
the crystallized polyester particles fed to the extrusion zone
after drying can contain low levels of residual acetaldehyde (as
measured by the French National Standard Test), such as 10 ppm or
less, 5 ppm or less, 2 ppm or less, or even 1 ppm or less. The
sheet or molded part can be further processed to make thermoformed
or blowmolded containers.
[0086] The present invention also provides a polymer blend
comprising a polyester of the invention and one or more additional
polymers, such as polyalkylene terephthalates and polyalkylene
naphthalates, along with other thermoplastic polymers such as
polycarbonate and polyamides.
[0087] The present invention also provides a composition comprising
the polyester of the invention and one or more additives. Additives
can be added to the melt phase or to the polyester to enhance its
performance properties. For example, one or more of the following
compounds can be used as additives in the polyesters of the
invention: colorants, pigments, glass fibers, crystallization aids,
impact modifiers, surface lubricants, denesting agents,
stabilizers, antioxidants, ultraviolet light absorbing agents,
metal deactivators, nucleating agents, acetaldehyde lowering
compounds, flame retardants, recycling release aids, oxygen
scavenging materials, platelet particles, reheat rate enhancing
aids such as elemental antimony or reduced antimony or reducing
agents to form such species in situ, silicon carbide, carbon black,
graphite, activated carbon, titanium nitride, black iron oxide, red
iron oxide and the like, sticky bottle additives such as talc, and
fillers and the like. The resin may also contain small amounts of
branching agents such as trifunctional or tetrafunctional
carboxylic acids or their derivatives or alcohols such as
trimellitic anhydride, trimethylol propane, pyromellitic
dianhydride, pentaerythritol, and other polyester forming polyacids
or polyols generally known in the art.
[0088] In addition to being used to manufacture containers (e.g.,
bottles), the polyesters of the invention can be also be used to
make sheets, films, trays, rods, tubes, lids, fibers, filaments
(such as bulk continuous filaments), other injection molded
articles, and any other appropriate molded, extruded, or
thermoformed article.
[0089] Beverage bottles made from polyethylene terephthalate
suitable for holding water or carbonated beverages, and heat set
beverage bottles suitable for holding beverages that are hot filled
into the bottle, are examples of the types of bottles that can be
made from the crystallized pellet of the invention.
[0090] The following examples are presented to further illustrate
certain aspects of the polyesters and methods disclosed herein.
However, these examples are not to be considered as limiting the
invention.
EXAMPLES
Example 1 (Comparative)
[0091] A polyester was prepared comprising terephthalic acid
residues and ethylene glycol residues with about 3.09 mol % of
cyclohexane dimethanol residues and about 3.38 mol % (1.83 wt %) of
diethylene glycol residues. The inherent viscosity of the polyester
was about 0.725 dL/g. The inherent viscosity was measured at
25.degree. C. using 0.5 grams of polymer per 100 mL of a solvent
consisting of 60% by weight phenol and 40% by weight of
tetrachloroethane. The intrinsic viscosity corresponding to this
inherent viscosity is about 0.762 dL/g. The ratio (on a mol %
basis) of cyclohexane dimethanol to diethylene glycol was about
0.91:1.0.
Example 2
[0092] A polyester was prepared in the same manner as in
Comparative Example 1 comprising terephthalic acid residues and
ethylene glycol residues with about 3.80 mol % of cyclohexane
dimethanol residues and about 2.0 mol % (1.08 wt %) of diethylene
glycol residues. The inherent viscosity of the polyester was about
0.724 dL/g and the corresponding intrinsic viscosity value was
about 0.761 dL/g. The ratio (on a mol % basis) of cyclohexane
dimethanol to diethylene glycol was about 1.90:1.0.
Example 3
[0093] A polyester was prepared in the same manner as in
Comparative Example 1 comprising terephthalic acid residues and
ethylene glycol residues with about 3.76 mol % of cyclohexane
dimethanol residues and about 2.02 mol % (1.09 wt %) of diethylene
glycol residues. The inherent viscosity of the polyester was about
0.718 dL/g and the corresponding intrinsic viscosity value was
about 0.754 dL/g. The ratio (on a mol % basis) of cyclohexane
dimethanol to diethylene glycol was about 1.86:1.0.
[0094] Differential scanning calorimetry was used to evaluate the
crystallization rate of the polyester resins. A scan rate of
20.degree. C./min was employed. The temperature corresponding to
the peak of the crystallization exotherm on the cooling scan was
recorded.
[0095] Freeblow volume was used as a measurement of the natural
stretch ratio of the polymer. The freeblow test was performed on 54
g 2 L preforms, soaked in boiling water for 180 s prior to the
application of about 70 psig air for about 60 s. The resulting
freeblow bottles were filled with water, capped, and weighed. The
weight of the preform and the cap were subtracted, and the
resulting net weight was converted to volume using an assumed
density of water of 1 g/cc. The reported results are averages of 24
measurements.
[0096] The fill time was recorded for the injection molding of the
resins on a Husky LX160 injection molding machine with an 8 cavity
injection mold making 24.6 g preforms. The barrel temperature
setpoints were 280.degree. C. with a transition to hold on position
at 20 mm. The fill speed was 80% and the fill pressure was 33%.
Fill times were recorded from machine output on the control panel
display. The reported results are averages of 19 measurements.
[0097] The peak fill pressure was recorded for the injection
molding of the resins on a Husky LX160 injection molding machine
with an 8 cavity injection mold making 24.6 g preforms. The barrel
temperature setpoints were 280.degree. C. with a transition to hold
on position at 20 mm. The fill speed was 33% and the fill pressure
was 60%. Peak fill pressures were recorded from observation of
machine output on the control panel display. The reported results
are averages of 19 measurements.
TABLE-US-00001 TABLE 1 Peak fill Freeblow pressure Material Tcc
(.degree. C.) Volume (cc) Fill time (s) (psi) Comparative 151 3247
1.97 226.6 Example 1 Example 2 153 2958 2.00 228.9 Example 3 151
3087 1.98 220.5
[0098] The fill time result for Comparative Example 1 is
inconsistent with the other data and is thought to have been
influenced by excessive moisture accumulated on the pellets after
drying and before injection molding. Preforms were not retained,
thus intrinsic viscosity measurements to validate this theory were
not possible.
[0099] The compositions of Examples 2 and 3 were chosen to yield
very similar crystallization behavior to that of the composition of
Comparative Example 1. However, the composition of Example 2 led to
a decrease in the natural stretch ratio, as measured by freeblow
volume, relative to that of Comparative Example 1. As demonstrated
in Example 3, a reduction in the intrinsic viscosity mitigated the
impact of the composition change on the freeblow volume, and led to
demonstrated improvements in the injection molding fill time or
reduction in the peak fill pressure during injection molding.
Further reduction of the intrinsic viscosity can lead to more
pronounced benefits in reduced fill time or reduced peak fill
pressure, while yielding a material of similar stretching
characteristics to the composition of Comparative Example 1. In one
embodiment of the invention, the lower the DEG content of the
polyester, the higher the reduction in intrinsic viscosity that can
be achieved, while maintaining favorable stretching characteristics
for use in conventional water bottle preform designs.
[0100] Currently, for state of the art injection molding machines
making preforms for water bottles, a 0.02 s reduction in fill time
would be worth on the order of $38,000 per machine per year.
Example 4 (Comparative)
[0101] A polyester was prepared comprising terephthalic acid
residues and ethylene glycol residues with about 12 mol % of
cyclohexane dimethanol residues and about 2.7 mol % (1.5 wt %) of
diethylene glycol residues. The inherent viscosity of the polyester
was about 0.691 dL/g and the corresponding intrinsic viscosity
value was about 0.725 dL/g. The ratio (on a mol % basis) of
cyclohexane dimethanol to diethylene glycol was about 4.44:1.0.
Example 5 (Comparative)
[0102] A polyester was prepared comprising terephthalic acid
residues and ethylene glycol residues with about 31 mol % of
cyclohexane dimethanol residues and about 2.7 mol % (1.5 wt %) of
diethylene glycol residues. The inherent viscosity of the polyester
was about 0.755 dL/g and the corresponding intrinsic viscosity
value was about 0.796 dL/g. The ratio (on a mol % basis) of
cyclohexane dimethanol to diethylene glycol was about
11.48:1.0.
TABLE-US-00002 TABLE 2 Freeblow Volume Material Tcc (.degree. C.)
(cc) Comparative 157 Not able to blow Example 4 without tearing
Comparative Not Not able to blow Example 5 detectable without
tearing
[0103] The polyesters compositions of Comparative Examples 4 and 5
with greater than 10 mol % modification were not able to be
successfully blown into freeblow shapes, indicating a lack of
strain hardening. These compositions are not suitable for the
stretch blow molding process used when making containers with the
materials of the present invention.
* * * * *